1. Field of the Invention
The invention relates generally to the fields of semiconductor fabrication, lithography, and polymer chemistry. More particularly, the invention relates to rare-earth photoresist compositions and a method of making the same. The product is suitable for use in visible light lithography.
2. Description of the Related Art
In the manufacture of patterned devices, such as semiconductor chips and packaging applications, the process of etching different layers which constitute the finished product is among the most crucial steps involved. One method widely employed in the etching process is to overlay the surface to be etched with a suitable photoresist, and then to immerse the substrate and photoresist in a chemical solution which attacks the substrate to be etched while leaving the photoresist intact. There are two types of photoresists: i) a positive resist is one which on exposure to imaging light is capable of being rendered soluble in a solvent in which the unexposed resist is not soluble, ii) a negative resist is one which is capable of polymerizing and/or insolubilizing upon exposure to imaging light. Typically, the exposing light for an UV photoresist, is a mercury vapor source emitting a broadband emission in the ultraviolet region which comprises of G line at 436 nm, H line at 405 nm and I line at 365 nm. Generally, the major output wavelength of the source is an I line at 365 nm. Recent research in the field of lithography is oriented towards the search for photoresist compositions that are sensitive to laser light. Deep-UV (DUV) lithography uses 248 nm and 193 nm exposure wavelengths supplied by KrF and ArF excimer lasers. Extreme ultraviolet (EUV) lithography, working at 13.5 nm with soft X-ray plasma sources, is under development. Dedicated photoresists for each wavelength have been devised. Examples of conventional resins for photoresists are phenol resins in which a part or the whole of hydroxyl groups are protected by groups such acetal or ketal (KrF photoresist), methacrylic acid resins in which an acid-labile ester group is introduced to carboxyl group (ArF photoresist) and the like.
The photosensitivity of photoresists is brought up to a practical value by addition of photosensitizers. U.S. Pat. No. 5,225,312 to Dixit et al. discloses a positive photoresist with coumarin dyes. In addition, examples of some photoresists with other organic dyes are provided in U.S. Pat. Nos. 6,376,150 to Bolli et al.; 5,976,770 to Sinta et al.; 5,128,232 to Thackeray et al.; and 5,492,790 to Hishiro.
E. Pavel et al. has published in Optics Communications 291 (2013) 259-263 a method describing “2 nm Quantum Optical Lithography” by application of quantum multiphoton confinement effect in fluorescent photosensitive glass-ceramics containing rare-earths. The breaking of the diffraction limit was possible by using novel materials such as fluorescent photosensitive glass-ceramics.
The benefit of the present invention is the replacement of high intensity light sources with low power laser diodes.
The object of the present invention is to provide a photoresist with improved sensitivity to visible light. In order to accomplish this object, there is provided a composition which contains rare-earth (RE) compounds.
It is believed, therefore, that a new photoresist composition will represent a significant advancement in the art.